This invention relates to photographic film cassettes and, more particularly, it concerns a multipart film cassette structure and method of assembly particularly suited for two component film systems having unique requirements for handling not only during manufacture, but also during packaging and storage up to the time the two film components are processed to provide a photographic image.
Commonly assigned U.S. Pat. No. 3,907,563 issued to Edwin H. Land on Sept. 23, 1975, discloses a diffusion transfer process in which the image-receiving element or sheet is impregnated with an alkaline processing composition. The image receiver or positive sheet includes a transparent support through which the final image may be observed in an image-receiving coating or layer directly on the transparent support. Reflectivity for use of the system as a positive print is provided by a white pigmented layer backed by an opaque layer. The three layers thus provided on the transparent support are impregnated with a liquid alkaline processing agent common to diffusion transfer film processing.
The negative element of the system disclosed in the aforementioned patent includes a support of mylar or similar material which may be either transparent or opaque. The negative support is coated by a polymeric acid layer, a timing layer, a dye developer layer and finally a silver halide layer. After exposure of the silver halide layer on the negative, the two sheets are brought together in intimate face-to-face contact as a laminate with the several coatings situated between the respective negative and positive sheet supports. The processing agent operates to transfer the latent image formed by exposure of the silver halide layer of the negative to the image-receiving layer directly behind the transparent support of the receiver sheet. The acid layer in the original negative sheet neutralizes the alkaline processing fluid, but under the control of the timing interlayer situated between the acid layer and the remaining layers of the composite laminate.
The diffusion transfer system disclosed in U.S. Pat. No. 3,907,563 is especially attractive from the standpoint of attaining high quality photographs with virtually no added requirements for assuring uniformity of processing fluid spread between the respective negative and positive elements other than impregnation of the positive element during manufacture. In this respect, it is to be noted that in substantially all commercially available diffusion transfer film systems, the alkaline processing fluid is initially contained by a rupturable pod, carried as a component of the film assembly, to be spread between the negative and positive elements of the film assembly after negative exposure. The uniformity of the spread requries precision not only in the processing apparatus, which is incorporated as a part of a camera or equivalent, but also a sophisticated and expensive combination of elements in the film sheet assembly itself.
While a film system of the type disclosed in U.S. Pat. No. 3,907,563 has potential for significant reduction in costs over current diffusion transfer systems, particularly in the manufacture of film, use of such film on a commercial basis is not without problems. Because of the strongly alkaline character of the processing agent and the need for its neutralization after processing, the components carrying the processing agent and the neutralizing acid layer must be kept separate until the processing step is performed. Also, it is important that the liquid processing agent in the positive sheet element be kept from evaporization and that the pH level of the liquid be maintained. Moreover, these conditions must be maintained not only for the normal shelf life of commercial photographic film, but also after the film is loaded into and stored in the camera.
In a copending U.S. application entitled "Method and Apparatus for Photographic Film System with Web Carried Processing Liquid", patent application Ser. No. 747,899 filed herewith, the aforementioned problems are addressed by the provision of a cassette system in which separate chambers are provided on opposite ends of a central tray-like section to receive the respective negative and processing element of the film system. The central tray-like section serves to retain the negative element of the system in an exposure plane, and the processing web chamber or positive chamber is equipped with a releasable stopper to ensure that the positive element, coated or otherwise wetted with a liquid processing agent, is hermetically encapsulated at all times other than during passage of the positive element from the chamber.
While the system disclosed in the aforementioned copending application shows great potential for commercial adaptation of the described two component film system, there is need for structural adaptation of the cassette system to low cost construction and/or assembly as well as to the discrete peculiarities of the positive and negative elements of such film systems. For example, the negative element of the film system is light sensitive and therefore must be manufactured and handled through packaging in plant facilities by experienced personnel using specialized equipment incident to the handling of light-sensitive material. Also, that portion of the cassette structure employed to house the negative element must be made from materials configured exclusively to the maintenance of a dark chamber for the negative film element. The processing web or positive is not light sensitive, but must be maintained at all times under conditions which prevent or inhibit the evaporation of the liquid processing agent. As a result of this latter characteristic, packaging assembly of the positive element in the cassette is more complex. Therefore, packaging of the positive element cannot only accommodate, but also requires different assembly equipment than that required for packaging the negative element. Also, the positive element, in general, is most efectively handled with visible access in light from which the negative must remain protected.